Blackberry Coffee Cake with Brown Butter Streusel (Bakery-Style)

Cake:

• 1/2 cup (113g) unsalted butter
• 1/2 cup (100g) granulated sugar
• 1/4 cup (55g) light brown sugar
• 2 large eggs
• 1 egg yolk
• 1 tbsp pure vanilla extract
• 1/2 cup (120g) sour cream
• 1/4 cup (60g) whole milk
• 1 1/2 cups (180g) all-purpose flour
• 1 1/2 tsp baking powder
• 1/4 tsp baking soda
• 1/4 tsp salt

Jammy Blackberries:

• 2 cups (313g) blackberries
• 2 TBSP granulated sugar
• 1 tsp lemon juice
• 1 tsp cornstarch
• 1 tsp cold water

Brown Butter Streusel

• 6 TBSP (85g) unsalted butter
• 1/2 cup (110g) light brown sugar
• 1/4 cup (50g) granulated sugar
• 1 cup (120g) all-purpose flour
• 1/2 tsp vanilla extract
• pinch of kosher salt
• zest of half of lemon (optional) 

Topping:

• 1/4 cup (30g) powdered sugar

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1. Prepare the Blackberry Layer
   In a saucepan, combine blackberries, sugar, and lemon juice. Cook over medium heat until berries soften and release their juices.
   In a small bowl, whisk cornstarch with water, then stir into the pan. Cook 1 to 2 minutes until thick and jammy.
   When you drag a spoon through the mixture, it should leave a clear streak that slowly fills back in.
   Set aside to cool (or refrigerate).
2. Brown the Butter
   In a light-colored saucepan, melt butter over medium heat. Cook until foamy, golden, and nutty, about 5 to 7 minutes.
   Pour into a heatproof bowl and cool until warm but not hot.
   (See notes for browning all the butter for the batter and streusel at once.)
3. Make the Streusel
   In a bowl, mix brown sugar, granulated sugar, flour, salt, and lemon zest.
   Add the portion of browned butter and vanilla. Mix until crumbly.
   Use your hands to form both large and small clumps.
   Refrigerate while preparing the batter.
4. Make the Cake Batter
   Preheat oven to 350°F (175°C). Line a 9-inch round pan with parchment.
   Whisk browned butter with granulated and brown sugar.
   Add eggs, yolk, vanilla, sour cream, and milk. Whisk until smooth.
   In a separate bowl, whisk flour, baking powder, baking soda, and salt.
   Fold dry ingredients into wet until just combined. Do not overmix.
5. Assemble
   Spread about 3/4 of the batter evenly in the pan.
   Spoon blackberry filling over top and gently swirl.
   Carefully spread remaining batter over the jam. Some mixing is fine.
   Sprinkle streusel evenly over the top.
6. Bake
   Bake 40 to 45 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.
   Cool in the pan for 30 minutes, then transfer to a wire rack to cool completely.
   Dust with powdered sugar before serving.

Notes:

Browning All the Butter at Once

You can brown all the butter together for the batter and streusel.

• Total butter: 198g
• Use 57% for batter (about 113g)
• Use 43% for streusel (about 85g)

After browning, weigh and divide using this ratio, since some moisture is lost during browning and won't equal to 198g.

Storage & Make-Ahead

Storage

• Room temperature: Up to 2 days, covered
• Refrigerator: Up to 5 days
• Freezer: Wrap tightly and freeze up to 2 months

Warm slices briefly before serving for best texture.

Make-Ahead Tips

• Blackberry filling: Make up to 3 days ahead. Store airtight in the refrigerator.
• Streusel: Prepare 1 day ahead and refrigerate.
• Batter: Mix wet ingredients and refrigerate. Store dry ingredients separately at room temperature. Combine and bake the next day.

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